Producing benzophenone and related products

ABSTRACT

A stilbene, e.g., cis- and/or trans-stilbene or a substituted stilbene, is oxidized at an elevated temperature to produce benzophenone and a related product. Diphenylacetaldehyde, also produced, can be converted under the conditions of the invention to produce additional benzophenone. The reaction is effected at a temperature in the approximate range 50*-600*F, preferably 200*-400*F under a pressure of oxygen of from about 1 to 500 psig, preferably 20 to about 200 psig. A solvent, e.g., a carboxylic acid for example acetic acid or a halogenated compound for example chlorobenzene is employed. Also, a catalyst, e.g., trifluoroacetic acid and/or trichloroacetic acid can be employed. Further a cocatalyst which is an organic compound of a transition metal, e.g., cobalt acetylacetonate or vanadium naphthenate can also be employed. New compounds, e.g., hydrobenzoin monotrifluoroacetate, hydrobenzoin bistrifluoroacetate, benzoin trifluoroacetate are produced by the process of the invention.

United States Patent [1 1 Holtz [451 Aug. 12, 1975 PRODUCING BENZOPHENONE AND RELATED PRODUCTS Hans D. Holtz, Bartlesville, Okla.

[73] Assignee: Phillips Petroleum Company,

Bartlesville, Okla.

22 Filed: July 12, 1972 21 App1.No.: 271,031

[75] lnventor:

OTHER PUBLICATIONS Hawkins et al., Journal of Applied Chemistry, Vol. 6, Jan. 6, 1956, pp. 1-11.

Awasthy et al.. J.A.C.S.. 91:4/Feb. 12. 1969, pp.. 991-996.

Zahees et a1. Chem. Abstracts, Vol. 50, Mar. 25, 1956, 4862(d) at 4863(b).

Berti et a1. Chem. Abst.," Vol. 54, 1 l-60, 24542(a) at 24542(e).

Bridson-Jones, Chem. Abstract, Vol. 46, Oct. 10, 1952, 9053(g) at 9054(g).

Maruyama et a1. Chem. Abst., Vol. 56, Feb. 5, 1962, 2399(i).

Primary Examiner--Anton l-l. Sutto Assistant Exam'iner-Richard D. Kelly 57 ABSTRACT A stilbene, e.g., cisand/or trans-stilbene or a substituted stilbene, is oxidized at an elevated temperature to produce benzophenone and a related product. Diphenylacetaldehyde, also produced, can be converted under the conditions of the invention to produce additional benzophenone.

The reaction is effected at a temperature in the approximate range 50600F, preferably 200400F under a pressure of oxygen of from about 1 to 500 psig, preferably 20 to about 200 psig.

A solvent, e.g., a carboxylic acid for example acetic acid or a halogenated compound for example chlorobenzene is employed. Also, a catalyst, e.g., trifluoroacetic acid and/or trichloroacetic acid can be employed. Further a cocatalyst which is an organic compound of a transition metal, e.g., cobalt acetylacetonate or vanadium naphthenate can also be employed.

New compounds, e. g., hydrobenzoin monotrifluoroacetate hydrobenzoin bistrifluoroacetate, benzoin trifluoroacetate are produced by the process of the invention.

11 Claims, No Drawings PRODUCING BENZOPHENONE AND RELATED PRODUCTS This invention relates to the production of benzophenone. lt also relates to the production of novel products. e.g.. hydrobenzoin monotrifluoroacetate, hydrobenzoin bistrifluoroacetate and benzoin trifluoroacetate. In one of its aspects it relates to the production of benzophenone from a stilbene by an oxidation process. Further, the invention relates to the conversion of diphenylacetaldehyde to benzophenone.

In one of its concepts the invention provides a process for the conversion of a stilbene to benzophenone and to a related product as herein described by oxidizing the stilbene with oxygen at an elevated temperature preferably under pressure. In another of its concepts, the invention provides a process, as described, wherein the oxidation is effected in a carboxylic acid solvent such as acetic acid. In a still further concept of the invention, the oxidation is effected in the presence of a halogenated carboxylic acid such as trifluoroacetic acid and/or trichloroacetic acid. Further still another concept of the invention provides a process. as described, wherein an organic compound of a transition metal for example. a naphthenate o r acetylacetonate is employed as a cocatalyst.

l have discovered that benzophenone. and related products can be produced from stilbene under conditions of oxidation as herein described at an elevated temperature now preferred to be in the approximate range 2()()40()F with oxygen, now preferred to be under a pressure at least at the initiation of the operation, when conducted in a batchwise or continuous operation, of from about 20 psig to about 200 psig or somewhat higher.

The conversion of stilbene, in which the phenyl groups are on different carbon atoms, by the present oxidative process to benzophenone is indeed surprising and unexpected. Further. the conversion of diphenylacetaldehyde to benzophenone under the condi tions of the invention is also unexpected.

An object of the invention is to produce benzophenone. Another object of the invention is to produce hydrobenzoin monotrifluoroacetate, hydrobenzoin bistrifluoroacetate and benzoin trifluoroacetate. A further object of the invention is to provide a process for the oxidation ofa stilbene. Still another object of the invention is to provide a process for the conversion of a stilbene to benzophenone and a related product in the presence of a catalyst. A further object still of the invention is to provide a solvent for the reaction or 'reactions involved. Still another object of the invention is to provide a catalyticoxidation of stilbene to produce beniophenone and other products, as herein described, employing a cocatalyst.

According to the present invention a stilbene is oxidized with oxygen, preferably under pressure, and at an elevated temperature to produce benzophenone, benzaldehyde. benzoic acid and di'phenylacetaldehyde. Also according to the invention, diphenylacetaldehyde recovered from the reaction mass or from any other source can be converted under the conditions of the process of the invention to produce benzophenone. Also produced. as later described are hydrobenzoin monotrifluoroacetate, hydrobenzoin bistrifluoroacetate and benzoin trifluoroacetate.

By the term stilbene" I intend to include all the compounds having the following formula. including the cis and trans isomers thereof:

and halogen such as fluorine, chlorine and bromine 75 with at least 2 R radicals on each ring being hydrogen. lt is understood that stilbenes with combinations of the various substituents are also suitable for use in the present oxidative process. i

As solvents for use in this invention halogenated aro-' matic compounds, benzene, and carboxylic acids are suitable. For example, aryl chlorides and aryl fluorides are suitable and include chlorobenzene, fluorobenzene, orthodichlorobenzene, l,2,4-trichlorobenzene, 1,3,5- trichlorobenzene, meta-difluorobenzene, paradichlorobenzene, l-chloronaphthalene, lfluoronaphthalene, metadichlorobenzene; and th'e like or mixtures thereof. Suitable carboxylic acid solvents are described by the formula RCO- H wherein R is alkyl containing 1 to 4 carbon atoms. Suitable solvents in- 40 clude aceticacid. n-butyric acid, propionic acid,and

the like or mixtures thereof.

Suitable catalysts for the inventive process-are described by the formula wherein X is fluorine or chlorine. and n can be l-lO. Suitable catalysts include trifluoroacetic acid. perfluorobutyric acid, perfluorooctanoic acid and the like or mixtures thereof. Presently, trifluoroacetic acid is preferred. Other halogenated carboxylic acids such as trichloroacetic'acid can also be used in the present process.

Suitable cocatalysts for use in the inventive process are selected from the group of transition metals consisting of iron, copper, manganese, cobalt, chromium, vanadium, cerium. and titanium. Commercially available naphthenates or acetylacetonates of the above transition metals generally are used as a matter of convenience in the practice of this invention but other compositions containing the above transition metals or mixtures thereof can also be used.

in the practice of the present invention, if a carboxylic acid solvent such acetic acid is used. the use of a catalyst and cocatalyst is optional. If a haloaromatic solvent such as chlorobenzene is used. a catalyst is required and a cocatalyst is optional.

In the following table several of the various embodiments of the invention are summarized.

TABLE 1 Systems for the Oxidation of Stilbcnc* with *Bcnzophenonc and bcnlaldehyde are produced in significant quantities in the above runs. Benzoie acid was produced in relatively small amounts as shown by its isolation from two runs (see footnote to Table 11). Diphenylaeetaldchyde was detectable in significant amounts in lower temperature runs. i.e.. at

temperatures 200F (see Table IV).

In accordance with the present invention, embodiments 1-1V of Table l were carried out by a general pro cedure which involved charging the reactants to a glass-lined titanium autoclave, pressuring to a desired level with oxygen, and heating the system at a desired temperature for a specified time. Reaction was evidenced by the decrease in oxygen pressure as the stilbene was oxidized. It is to be noted that the O pressure reported herein was the initial pressure reading. As the oxygen pressure decreased during a run, the system was not repressured to maintain the initial oxygen pressure reading. The autoclave was cooled to room tempera- ,.ture and the mixture distilled to isolate the products.

Alternatively,-in a number of the experimental runs, the products were analyzed by glc after the addition of an internal standard. Example 1 below is a typical run and specifically illustrates embodiment IV of Table I. (See Run 1 1 in Table 11).

EXAMPLE 1 A mixture of trans-stilbene g, 5.55 X 10 mole), cobalt(ll) acety1acetonate (5 mg), chlorobenzene (75 m1), and trifluoroacetic acid 1.5 g) was placed in a glass lined titanium Parr Rocking Bomb and the system was pressured to 100 psig oxygen at room temperature. The system was heated to 350F and maintained at this temperature for a period of two hours. The bomb was cooled, vented, and the product mixture was analyzed by glc after the addition of 2.00 g methyl benzoate as an internal standard. According to the glc results, conversion of stilbene was about 86% and the efficiency to benzaldehyde and benzophenone, respectively, was

1 mole stilbene 1 mole stilbene l mole stilbene 1 mole stilbene 2 moles bcnzaldchydc 2 moles bcnzoic acid) 1 mole benzophenonc 1 mole diphenylacctaldehydc) The results of runs representative of embodiments 1, 11, Ill, and IV are disclosed in Table 11.

In Table 11 Run 4 indicates that embodiment I1 is not operable for stilbene oxidation at 150F in a reaction period of 4 hours.

Gas-liquid chromatography (glc) analyses were carried out on a 9 ft. 20% Apiezon L column programmed from 100C to about 250C. The detector was maintained at 300C and the sampler was 250C. The percent efficiency is based on the relative size of the various peaks compared to the size of the peak due to the presence of the internal standard. As is well known in the art, the identity of a component represented by a glc peak is established by condensing the effluent corresponding to each peak on its exit from the glc instrumen't. The effluent so obtained is then characterized by appropriate techniques such as elemental, nuclear magnetic resonance (NMR), infrared, ultraviolet and mass spectroscopic analyses and melting or boiling point. An illustrative run is described in Example 11 (See Run 3 in Table 11).

EXAMPLE ll This reaction was carried out in the same manner as described in Example 1 with the following charge:

TABLE ll Run 0 Time Stilbenc Efficiency* ml ml ml Embodi- No. T( F psi Hrs Conversion CHO d CO CF CO H rbCl HOAC ment 1 1 350 200 3 78.6 28 .31 O 0 2 350 0.66 68 26.4 31.2 0 0 75 ll 3 200 100 6 80.4 12.7 18.4 5.0 0 75 4 100 4 0 0 0 5.0 0 75 "I 5 350 50 2 40.3 27.2 46 1.0 75 0 6 350 100 3 6.7 51.3 56.8 0.1 75 0 7 350 100 2 54 24 39 0.5 75 0 x 350 50 2 36 39 47 0.5 75 0 9 350 50 2 41.5 36.5 47.8 0.5 75 0 l0 350 100 2 52.4 22.5 40.2 1.0 75 0 lV** 11 350 100 2 85.8 34 35.3 1.5 75 0 12 350 100 2 93 32.2 30.0 1.0 75 0 "As defined above.

"Cobalulh acctylacetonate and vanadium naphthcnate. respectively, were used in runs 1 l and I2.

transstilbene g, 5.55 X 10 mole), glacial acetic acid (75 ml) and trifluoroacetic acid (5.0 ml). The system was pressured to 100 psig O heated to 200F, and maintained at this temperature for a period of 6 hours. The reactor was cooled, vented and stripped of volatiles on a rotary evaporator. The residue was taken up in chlorobenzene and methylbenzoate was added as an internal standard before analyzing the product mixture by glc analysis. According to the glc analysis, the conversion of stilbene was 80.4% with a 7: efficiency. respectively, to benzaldehyde and benzophenone of 12.7% and 18.4%. The peak corresponding to benzoph enone was condensed on its exit from the glc instrument and analyzed by infrared analysis. The sample was thus shown to be mostly benzophenone contaminated with about 10% diphenylacetaldehyde.

In order to demonstrate the oxidation of stilbene over a range of temperatures from 300F to 100F, several runs were carried out using the efficiency to benzaldehyde as a measure of the oxidation of stilbene that was occurring. The results of these runs are shown in Table III.

TABLE III EXAMPLE IV /z C /PH Calcd 61.94 4.22 61.70 4.06

Found A sample of a monotrifluoroacetate of hydrobenzoin was prepared by the reaction of stilbene oxide with trifluoroacetic acid. The sample was characterized by ele- Oxidation of Stilbenc to Bcnzaldehyde* In all runs 1.0 ml CF;,(O. .H and 75 ml dzCl were used except in runs 19 and 20 in which 50 ml d Cl were used. The catalysts in runs 1) and 20 were. respectively. perlluorohutyric acid and perfluorixiclanic acid with cocatlyst vanadium naphthenate.

Example III,is given below to demonstrate that a charge of diphenylacetaldehyde, chlorobenzene, and trifluoroacetic acid in the present inventive oxidative process yields a mixture containing benzophenone.

EXAMPLE III This reaction was carried out in the same apparatus as used in Example I employing a charge of chlorobenzene (75 ml), trifluoroacetic acid (1.0 ml), and diphenylacetaldehyde (5 g). The system was pressured to 100 psig O- heated to 350F, and maintained at this temperature for a period of 3 hours. The reactor was cooled vented, and volatiles were stripped on a rotary evaporator. Distillation of the residue gave 3.63 g of a material which by infrared analysis was shown to be benzophenone in greater than 90% purity. A portion of this material was recrystallized from methanol to give a sample which exhibited an infrared spectrum which was identical to that of an authentic sample of benzophenone.

The following components were identified in product mixtures arising by the use of the present inventive process: hydrobenzoin monotrifluoroacetate, hydrobenzoin bis(trifluoroacetate), and benzoin trifluoroacetate. The presence of these components was verified as discussed below in Examples IV. V and VI.

mental analysis. Elemental analysis calculated for m ia a a 71C H 92F Calc'd 61.94 4.22 18.37 Found 62.0 4.13 18.2

An additional sample of a hydrobenzoin monotrifluoroacetate was prepared by the reaction of trifluoroacetic anhydride and hydrobenzoin. The nuclear magnetic resonance and infrared spectral properties of the three samples of hydrobenzoin monotrifiuoroacetate were identical.

The sample of a monotrifluoroacetate of hydrobenzoin was isolated from the combination of five runs which used a charge of stilbene, chlorobenzene, and trifluoroacetic acid. These runs were carried out in a glass reaction bulb attached to an oxygen reservoir by means of a stainless steel line. After charging the reactants, the bulb was attached to the stainless steel line, placed in a 50C bath, purged quickly three times with oxygen, and then pressured to about 45 psig O Reaction times for these five runs varied from 360 to 1825 minutes.

EXAMPLE v A sample of hydrobenzoin bis(trifluoroacetate) was isolated from a run which used a charge of stilbene,

chlorobenzcne. and trifluoroacetic acid (Embodiment Ill). This run was carried out in'the same apparatus used in Example I. The initial oxygen pressure was 100 psig. and the reaction was carried out at 150F for a pe is also to be ,noted that the detectable quantity of riod of 39 hours and 28 minutes. The reaction mixture 5 should be carried out at temperatures of 350F or was cooled. vented, and stripped of volatiles on a rotary higher. evaporator; The presence of the bisflrifluoroasewte) In the practice of the present invention, it is to be ester of hydiobehloih 3 established y using gle ahalnoted that safety considerations dictate against the use y ah APleZQh L e The ester Sample w of the upper end of the temperature range coupled with lated condensation Of the glC effluent and at l() the upper of the oxygen pressure range In gen. The er was Shown to be the bisurifluor' eral, the use of lower temperatures will require longer oaeetate) of hydrobenzoin by the fact that the Spectral reaction periods to attain a certain conversion at con- Propemes (both infrared and nuclear magnetic stant oxygen pressure and constant molar ratio of stilhahee) were identical to those of a blsurrlfllueroace' bene to trifluoroacetic acid. (e) Metal/stilbene ratio tate) of hydrobenzoin prepared below. A sample of the The transition metals in the present process ff bis(trifluoroacetate) of hydrobenzoin was prepared by tively promote the rate of stilbene Oxidation in the reaction of stilbene glycol with trifluoroacetic anamounts as low as Pan of meta] per million hydride- }Thls product melted at (MO-95C and e parts of stilbene. Presently, vanadium is preferred. characterized by elemental analysis. Elemental analysis Higher ratios of metal to stilbene can be used as Cakulated for CWHRFGO dictated by convenience and/or economics.

' It will be seen from the foregoing tabulation of reac- %H %F tion parameters that the temperature though preferred Cale-d 532 29 38.1 to be elevated can be as low as 50F at which rather Found 5375 272 small amounts of benzophenone will be produced. It i will also be seen that temperature can be quite high EXAMPLE VI that is well above 400 i.e. 600F or higher but that these temperatures best results will ordinarily not be A Sample of the trlfluol'oaeetme of benzoin was obtained. The now preferred range of temperature for lated from a combination of three runs carried out in the production of benzophenone is as earlier given accordance with Embodiment Ill of the present inven- 30 herein namely f about to about tion. These runs were carried out in the glass reactor Also it will be seen that the Oxygen pressure can be used in Example IV under approximately thesame quite low albeit it is now preferred to have an elevated P and Oxygen Pressure (48 pslg oxygen pressure especially when operating in batch or action times varied from 270 to 430 minutes. The reacautoclave mannen tion charge consisted of stilbene, chlorobenzene, and Reasonable variation and modification are possible trifluoroacetic acid. Isolation involved distillation of Within the Scope of the foregoing disclosure and the the volatiles in vacuo followed by elution column chropended Claims to the invention the essence of which is matography to Separate out a component whlch was that a stilbene is converted by oxidation with oxygen to identified by infrared analysis as benzoin trifluoroaceproduce benzophenone and related products, fig t 4O drobenzoin monotrifluoroacetate, hydrobenzoin bistri- Inlectlon of an m? Sample f monotnfluor' fluoroacetate and benzoin trifluoroacetate, in one emacetate 9 hydrobenzom mm e glc mstr'lument gave bodiment with a catalyst, in another with a catalyst. and to a P Correspondmg to dlphenxlacetaldehyde a cocatalyst, and preferably at an elevated temperature The diphenylacetaldehyde peak was trapped at the exit and under some pressure of oxygen of the glc instrument and its structure was verified by I Claim: mfrared f l. The oxidation of a stilbene under conditions to T f f parameters Sulmble'for the oxldanon P produce a benzophenone which comprises subjecting Stllbene accordance t the present process are said stilbene dissolved in a solvent selected from carcussed below so boxylic acids and halogenated aromatic compounds in v i the presence of a catalyst having the formula Preferred for the C,,X CO H wherein X is fluorine or chlorine and n Operable Pmductlo 0f deco can be 1-10, to the action of oxygen under pressure. (3) Temperature O 504) 300400 2. The oxidation of a stilbene according to claim 1 under the following conditions: a temperature in a It is to be noted that small amounts of benzophenone range of from about 200 to about 4()()F and under a are produced at temperatures well below 2()()F.'lt pressure of oxygen of from about 2()20() psig.

i I More Opcrablc ,Prcfcrrcd Preferred (b) Reaction time 1 min -418 v i 0 5-5 hrs (c) Molar Ratio f 'l :500 10:500.

stilhcnc/CF CO H in 'aryl halide solvent 1 (d) Oxygen pressure (psig) by l5 40- 201) 3. The production of benzophenone according to claim 1 wherein the stilbene is a compound having the including the cis and trans isomers and wherein each R can be selected from hydrogen, alkyl, alkoxy, or perfluoroalkyl radicals containing 1 to 4 carbon atoms,

and halogen such as fluorine, chlorine and bromine with at least 2 R radicals on each ring being hydrogen.

4. A process according to claim 1 wherein a halogenated aromatic compound is employed as solvent.

5. A process according to claim 1 wherein a carboxylic acid solvent is employed.

6. A process according to claim 1 wherein an organic compound of a transition metal selected from the group consisting of iron. copper, manganese, chromium, vanadium, cobalt, cerium and titanium is employed as a cocatalyst.

7. A process according to claim 6 wherein the cocatalyst is selected from cobalt acetylacetonate and vanadium naphthanate.

8. The oxidation of trans-stilbene, according to claim 1 wherein the trans-stilbene is heated under a pressure of oxygen in the presence of trifluoroacetic acid and cobalt acetylacetonate in the presence of chlorobenzene.

9. The oxidation of stilbene according to claim 1 wherein transstilbene is oxidized under a pressure of oxygen at an elevated temperature in the presence of glacial acetic acid.

10. The oxidation of stilbene according to claim 1 wherein transstilbene is oxidized in the presence of glacial acetic acid and trifluoroacetic acid.

11. The oxidation of diphenylacetaldehyde under a pressure of oxygen to produce benzophenone in the presence of trifluoroacetic acid and, as a solvent, chlorobenzene. 

1. THE OXIDATION OF A STILBENE UNDER CONDITIONS TO PRODUCE A BENZOPHENONE WHICH COMPRISES SUBJECTING SAID STIBENE DISSOLVED IN A SOLVENT SELECTED FROM CARBOXYLIC ACIDS AND HALOGENATED AROMATIC COMPOUNDS IN THE PRESENCE OF A CATALYST HAVING THE FORMULA CNX2N+1CO2H WHEREIN X IS FLOURINE OR CHLORINE AND N CAN BE 1-10, TO THE ACTION OF OXYGEN UNDER PRESSURE.
 2. The oxidation of a stilbene according to claim 1 under the following conditions: a temperature in a range of from about 200* to about 400*F and under a pressure of oxygen of from about 20-200 psig.
 3. The production of benzophenone according to claim 1 wherein the stilbene is a compound having the formula
 4. A process according to claim 1 wherein a halogenated aromatic compound is employed as solvent.
 5. A process according to claim 1 wherein a carboxylic acid solvent is employed.
 6. A process according to claim 1 wherein an organic compound of a transition metal selected from the group consisting of iron, copper, manganese, chromium, vanadium, cobalt, cerium and titanium is employed as a cocatalyst.
 7. A process according to claim 6 wherein the cocatalyst is selected from cobalt acetylacetonate and vanadium naphthanate.
 8. The oxidation of trans-stilbene, according to claim 1 wherein the trans-stilbene is heated under a pressure of oxygen in the presence of trifluoroacetic acid and cobalt acetylacetonate in the presence of chlorobenzene.
 9. The oxidation of stilbene according to claim 1 wherein transstilbene is oxidized under a pressure of oxygen at an elevated temperature in the presence of glacial acetic acid.
 10. The oxidation of stilbene according to claim 1 wherein transstilbene is oxidized in the presence of glacial acetic acid and trifluoroacetic acid.
 11. THE OXIDATION OF DIPHENYLACETALDEHYDE UNDER A PRESSURE OF OXYGEN TO PRODUCE BENZOPHENONE IN THE PRESENCE OF TRIFLUOROACETIC ACID AND, AS A SOLVENT, CHLOROBENZENE. 